1. Field of the Invention
This invention relates to a heat exchanger and, more particularly, to an arrangement for heat transfer tubes in the heat exchanger.
2. Description of the Related Art
A typical arrangement for closely packed heat transfer tubes in a heat exchanger is shown, for example, in U.S. Pat. No. 4,235,281issued to Fitch et al.. Referring to FIGS. 1 -3, a heat exchanger 10 comprises an upper tank 11, a lower tank 12, and a heat exchanger core 13 disposed between upper tank 11 and lower tank 12. Heat exchanger core 13 comprises a plurality of heat transfer tubes 15 spaced apart from each other and substantially parallel to one another. Upper tank 11 is divided into three chambers, such as first upper chamber 18, second upper chamber 19, and third upper chamber 20, by a first upper partition 11a and a second upper partition 11b. First upper partition 11a is perpendicular to a direction of air flow Q through heat exchanger core 13. Second upper partition 11b is parallel to air flow Q. First upper chamber 19 has the same capacity as third upper chamber 20.
Lower tank 12 is divided into two chambers, such first lower chamber 21 and second lower chamber 22 by lower partition 12a. First upper chamber 18 and third upper chamber 20 are respectively provided with inlet 16 and outlet 17 which connect heat exchanger 10 to an air conditioning system (not shown), i.e. a vehicle air conditioning system. Each of the plurality of heat transfer tubes 15 is joined at its opposite ends to upper tank 11 and lower tank 12.
A heat exchanger medium, a refrigerant for example, is introduced through inlet 16 into first upper chamber 18. The medium flows down through tubes 15 to first lower chamber 21 of lower tank 12. The medium then flows back up tubes 15 to second upper chamber 19. The medium then flows down tubes 15 to second lower chamber 22 and back up through tubes 15 to third upper chamber 20. The medium then exits the heat exchanger through outlet 17.
Generally, heat transfer tubes 15 are designed to be closely arranged so that the air flow Q, which passes across tubes 15, will strike each of the plurality of tubes 15. Generally, heat transfer tubes 15 cannot be connected to upper and lower tanks 11, 12 in the areas of partition portions 11a, 11b, and 12a. Therefore, tubes 15 are generally not disposed between tanks 11 and 12 in these areas. This absence of tubes creates a first pathway A along lower partition 12a and extending between upper and lower tanks 11, 12. A second pathway B is also created along partition 11a and extending between upper and lower tanks 11, 12. First pathway A is generally box-shaped and extends from a first end portion 13a of heat exchanger core 13 to a second end portion 13b of core 13. First pathway A is parallel to the direction of air flow Q. Second pathway B is also generally box-shaped and extends from a first side 13c of core 13 to a second side 13d of core 13. Second pathway B is generally perpendicular to air flow Q.
A volume of air flow, which passes through first pathway A, is generally greater than a volume of air flow which passes through the remaining space in heat exchanger core 13. Thus, a relatively large quantity of air can flow through heat exchanger 10 without exchanging heat with the medium flowing through the plurality of heat transfer tubes 15. As a result, the heat exchange efficiency of heat exchanger 10 is reduced.
Further, when a known heat exchanger is used as an evaporator, an evaporative capacity of the refrigerant cooling circuit is increased and, thus, a flow velocity of the circulating refrigerant is increased within the cooling circuit. As a result of the increased evaporative capacity and refrigerant flow velocity, refrigerant pressure tends to drop within the heat exchanger.